In microwave communication networks, there is always a challenge to obtain good performance given varying conditions in the physical environment in which the microwave link is deployed.
Microwave links have traditionally been configured for transmission at a fixed data rate, i.e., using a fixed modulation and coding scheme; or in other words set for a fixed scenario with certain margin to guarantee a certain data transport capacity and link availability.
The fixed modulation and coding scheme is usually set for a worst case scenario representing transmission conditions which only occur very seldom. When the transmission conditions of a fixed rate microwave link are improved, there is no impact on the data transport capacity of the microwave link. In a case with deteriorated transmission conditions, the quality of the channel may fall below what is required for the given modulation and coding scheme and the link will be unavailable, i.e., the link will go down. The traffic flows affected by the link down state may in many instances be redirected over other links in a network.
Some microwave link based networks implement the possibility of so-called adaptive coding and modulation, ACM or adaptive coding, modulation and baud rate; in the following presented as ACM(B). Using ACM(B), the transmission rate of a microwave link is adapted to current propagation conditions in real-time; when channel conditions of the link are favorable a higher transmission rate is used and when conditions link deteriorate, e.g., due to changing weather conditions, the transmission rate is decreased to a lower transmission rate.
The use of ACM(B) at least in theory provides an improved microwave link network, since coding and modulation are adjusted according to current RF propagation conditions. However, during shifting propagation conditions, microwave links in a network may change offered data rates over a large range which can lead to instability on a network level. Therefore, in order to provide a stable network, microwave links are often configured to only offer ACM(B) over a limited range of data rates, or not at all.
When propagation conditions go below a threshold level, the microwave link, as mentioned above, may go down. This is not a preferred event, since the effort of re-activating the link may be time-consuming. Therefore, there is a need to provide a solution that enables quick recovery of a microwave link following radio link failure, while maintaining network stability.